The dominant semiconductor technology used for the manufacture of ultra-large scale integrated (ULSI) circuits is the metal-oxide-semiconductor field effect transistor (MOSFET) technology. Reduction in the size of MOSFETs has provided continued improvement in speed, performance, circuit density, and cost per unit function over the past few decades. As the gate length of the conventional bulk MOSFET is reduced, the source and drain increasingly interact with the channel and gain influence on the channel potential. Consequently, a transistor with a short gate length suffers from problems related to the inability of the gate to substantially control the on and off states of the channel.
Phenomena such as reduced gate control associated with transistors with short channel lengths are termed short-channel effects. Increased body doping concentration, reduced gate oxide thickness, and ultra-shallow source/drain junctions are ways to suppress short-channel effects. However, for device scaling well into the N2x nm regime, approaches involving the use of fin field-effect transistors (finFETs) are being investigated to improve the short channel effects.
Generally, fins are produced by etching a trench in a silicon substrate. A liner of in-situ steam generation (ISSG) oxide is formed along the sidewalls of the trench, and then the trench is filled by a high-density plasma (HDP) oxide or a high-aspect-ratio process (HARP) oxide. An etch-back process is typically performed to recess the oxide within the trench, thereby forming the fins. During the etch-back process, however, oxide fences are often formed along sidewalls of the trench due to the differences in the etch rate between the liner oxide and the HDP/HARP oxide. The oxide fences may result in a thinner gate oxide or bottom oxide and may adversely impact the gate leakage performance of the finFETs.
As a result, a structure of and method for forming semiconductor devices having fins with no or reduced oxide fences are needed.